Add 'nix dev-shell' and 'nix print-dev-env' command
'nix dev-shell' is intended to replace nix-shell. It supports flakes, e.g. $ nix dev-shell nixpkgs:hello starts a bash shell providing an environment for building 'hello'. Like Lorri (and unlike nix-shell), it computes the build environment by building a modified top-level derivation that writes the environment after running $stdenv/setup to $out and exits. This provides some caching, so it's faster than nix-shell in some cases (especially for packages with lots of dependencies, where the setup script takes a long time). There also is a command 'nix print-dev-env' that prints out shell code for setting up the build environment in an existing shell, e.g. $ . <(nix print-dev-env nixpkgs:hello) https://github.com/tweag/nix/issues/21
This commit is contained in:
Eelco Dolstra
parent
4588a6ff3c
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2b8c63f303
276
src/nix/shell.cc
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276
src/nix/shell.cc
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#include "eval.hh"
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#include "command.hh"
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#include "common-args.hh"
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#include "shared.hh"
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#include "store-api.hh"
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#include "derivations.hh"
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#include "affinity.hh"
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#include "progress-bar.hh"
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using namespace nix;
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struct BuildEnvironment
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{
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// FIXME: figure out which vars should be exported.
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std::map<std::string, std::string> env;
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std::map<std::string, std::string> functions;
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};
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BuildEnvironment readEnvironment(const Path & path)
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{
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BuildEnvironment res;
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auto lines = tokenizeString<Strings>(readFile(path), "\n");
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auto getLine =
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[&]() {
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if (lines.empty())
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throw Error("shell environment '%s' ends unexpectedly", path);
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auto line = lines.front();
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lines.pop_front();
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return line;
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};
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while (!lines.empty()) {
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auto line = getLine();
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auto eq = line.find('=');
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if (eq != std::string::npos) {
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std::string name(line, 0, eq);
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std::string value(line, eq + 1);
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// FIXME: parse arrays
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res.env.insert({name, value});
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}
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else if (hasSuffix(line, " () ")) {
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std::string name(line, 0, line.size() - 4);
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// FIXME: validate name
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auto l = getLine();
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if (l != "{ ") throw Error("shell environment '%s' has unexpected line '%s'", path, l);
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std::string body;
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while ((l = getLine()) != "}") {
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body += l;
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body += '\n';
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}
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res.functions.insert({name, body});
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}
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else throw Error("shell environment '%s' has unexpected line '%s'", path, line);
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}
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return res;
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}
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/* Given an existing derivation, return the shell environment as
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initialised by stdenv's setup script. We do this by building a
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modified derivation with the same dependencies and nearly the same
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initial environment variables, that just writes the resulting
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environment to a file and exits. */
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BuildEnvironment getDerivationEnvironment(ref<Store> store, Derivation drv)
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{
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auto builder = baseNameOf(drv.builder);
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if (builder != "bash")
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throw Error("'nix shell' only works on derivations that use 'bash' as their builder");
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drv.args = {"-c", "set -e; if [[ -n $stdenv ]]; then source $stdenv/setup; fi; set > $out"};
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/* Remove derivation checks. */
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drv.env.erase("allowedReferences");
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drv.env.erase("allowedRequisites");
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drv.env.erase("disallowedReferences");
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drv.env.erase("disallowedRequisites");
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// FIXME: handle structured attrs
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/* Rehash and write the derivation. FIXME: would be nice to use
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'buildDerivation', but that's privileged. */
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auto drvName = drv.env["name"] + "-env";
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for (auto & output : drv.outputs)
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drv.env.erase(output.first);
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drv.env["out"] = "";
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drv.env["outputs"] = "out";
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drv.outputs["out"] = DerivationOutput("", "", "");
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Hash h = hashDerivationModulo(*store, drv);
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Path shellOutPath = store->makeOutputPath("out", h, drvName);
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drv.outputs["out"].path = shellOutPath;
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drv.env["out"] = shellOutPath;
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Path shellDrvPath2 = writeDerivation(store, drv, drvName);
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/* Build the derivation. */
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store->buildPaths({shellDrvPath2});
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assert(store->isValidPath(shellOutPath));
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return readEnvironment(shellOutPath);
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}
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struct Common : InstallableCommand
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{
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/*
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std::set<string> keepVars{
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"DISPLAY",
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"HOME",
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"IN_NIX_SHELL",
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"LOGNAME",
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"NIX_BUILD_SHELL",
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"PAGER",
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"PATH",
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"TERM",
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"TZ",
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"USER",
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};
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*/
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std::set<string> ignoreVars{
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"BASHOPTS",
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"EUID",
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"NIX_BUILD_TOP",
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"PPID",
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"PWD",
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"SHELLOPTS",
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"SHLVL",
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"TEMP",
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"TEMPDIR",
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"TMP",
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"TMPDIR",
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"UID",
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};
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void makeRcScript(const BuildEnvironment & buildEnvironment, std::ostream & out)
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{
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for (auto & i : buildEnvironment.env) {
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// FIXME: shellEscape
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// FIXME: figure out what to export
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// FIXME: handle arrays
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if (!ignoreVars.count(i.first) && !hasPrefix(i.first, "BASH_"))
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out << fmt("export %s=%s\n", i.first, i.second);
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}
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for (auto & i : buildEnvironment.functions) {
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out << fmt("%s () {\n%s\n}\n", i.first, i.second);
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}
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// FIXME: set outputs
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out << "export NIX_BUILD_TOP=\"$(mktemp -d --tmpdir nix-shell.XXXXXX)\"\n";
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for (auto & i : {"TMP", "TMPDIR", "TEMP", "TEMPDIR"})
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out << fmt("export %s=\"$NIX_BUILD_TOP\"\n", i);
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}
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};
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std::pair<AutoCloseFD, Path> createTempFile(const Path & prefix = "nix")
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{
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Path tmpl(getEnv("TMPDIR", "/tmp") + "/" + prefix + ".XXXXXX");
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// Strictly speaking, this is UB, but who cares...
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AutoCloseFD fd(mkstemp((char *) tmpl.c_str()));
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if (!fd)
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throw SysError("creating temporary file '%s'", tmpl);
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return {std::move(fd), tmpl};
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}
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struct CmdDevShell : Common
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{
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std::string name() override
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{
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return "dev-shell";
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}
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std::string description() override
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{
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return "run a bash shell that provides the build environment of a derivation";
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}
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Examples examples() override
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{
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return {
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Example{
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"To get the build environment of GNU hello:",
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"nix dev-shell nixpkgs:hello"
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},
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Example{
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"To get the build environment of the default package of flake in the current directory:",
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"nix dev-shell"
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},
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};
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}
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void run(ref<Store> store) override
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{
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auto drvs = toDerivations(store, {installable});
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if (drvs.size() != 1)
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throw Error("'%s' needs to evaluate to a single derivation, but it evaluated to %d derivations",
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installable->what(), drvs.size());
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auto & drvPath = *drvs.begin();
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auto buildEnvironment = getDerivationEnvironment(store, store->derivationFromPath(drvPath));
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auto [rcFileFd, rcFilePath] = createTempFile("nix-shell");
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std::ostringstream ss;
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makeRcScript(buildEnvironment, ss);
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ss << fmt("rm -f '%s'\n", rcFilePath);
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writeFull(rcFileFd.get(), ss.str());
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stopProgressBar();
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auto shell = getEnv("SHELL", "bash");
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auto args = Strings{baseNameOf(shell), "--rcfile", rcFilePath};
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restoreAffinity();
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restoreSignals();
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execvp(shell.c_str(), stringsToCharPtrs(args).data());
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throw SysError("executing shell '%s'", shell);
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}
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};
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struct CmdPrintDevEnv : Common
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{
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std::string name() override
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{
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return "print-dev-env";
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}
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std::string description() override
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{
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return "print shell code that can be sourced by bash to reproduce the build environment of a derivation";
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}
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Examples examples() override
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{
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return {
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Example{
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"To apply the build environment of GNU hello to the current shell:",
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". <(nix print-dev-env nixpkgs:hello)"
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},
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};
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}
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void run(ref<Store> store) override
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{
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auto drvs = toDerivations(store, {installable});
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if (drvs.size() != 1)
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throw Error("'%s' needs to evaluate to a single derivation, but it evaluated to %d derivations",
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installable->what(), drvs.size());
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auto & drvPath = *drvs.begin();
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auto buildEnvironment = getDerivationEnvironment(store, store->derivationFromPath(drvPath));
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stopProgressBar();
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makeRcScript(buildEnvironment, std::cout);
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}
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};
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static RegisterCommand r1(make_ref<CmdPrintDevEnv>());
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static RegisterCommand r2(make_ref<CmdDevShell>());
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